Rubber goods such as tire treads often are made from elastomeric compositions that contain one or more reinforcing materials such as, for example, particulate carbon black and silica; see, e.g., The Vanderbilt Rubber Handbook, 13th ed. (1990), pp. 603-04.
Good traction and resistance to abrasion are primary considerations for tire treads; however, motor vehicle fuel efficiency concerns argue for a minimization in their rolling resistance, which correlates with a reduction in hysteresis and heat build-up during operation of the tire. These considerations are, to a great extent, competing and somewhat contradictory: treads made from compositions designed to provide excellent road traction, particularly in wet conditions, tend to exhibit increased rolling resistance while those designed to minimize rolling resistance might provide only acceptable traction performance.
Filler(s), polymer(s), and additives typically are chosen so as to provide an acceptable balance of these properties. Ensuring that reinforcing filler(s) are well dispersed throughout the polymeric material(s) both enhances processability and acts to improve physical properties. Dispersion of fillers can be improved by increasing their interaction with the polymer(s) and/or decreasing their interaction with each other. Examples of efforts of this type include high temperature mixing in the presence of selectively reactive promoters, surface oxidation of compounding materials, surface grafting, and chemically modifying the polymer, typically at a terminus thereof.
Many of the polymers used in the manufacture of vulcanizates such as, e.g., tire components, are elastomeric. In addition to natural rubber, some of the most commonly employed include high-cis polybutadiene, often made by processes employing Ziegler-Natta catalysts, and substantially random styrene/butadiene interpolymers, often made by processes employing anionic initiators. Chemical modifications that can be undertaken with carbanionic polymers often do not work for polymers made via catalytic processes.